Alternating current voltage regulator including system no-load to fullload compensating means



S N A E M Lm mm ES w mm Sm mm w HU F MO .T R D u 4 m March 19, 1968 ALTERNATINQ CURRENT VOLTAGE REGULATOR INCLUDING SYSTEM 4 Sheets-Sheet 1.

Filed May 13, 1965 MA/N LOAD jzi/erzfars. $05495 Jli iansazt Mm! 260%44'20. 3y PEt/VERRI JJE 0 MIME! I March 19 Filed May 15, 1965 1968 R. M. HENDERSON ETAL 8 ALTERNATING CURRENT VOLTAGE REGULATOR INCLUDING SYSTEM NO-LOAD TO FULL-LOAD COMPENSATING MEANS 4 SheetsSheet 2 MA IN LOAD CURRENT ZE/VER REFERENCE TIME March 19, 1968 R. M. HENDERSON ETAL 3,374,418

ALTERNATING CURRENT VOLTAGE REGULATOR INCLUDING SYSTEM NO-LOAD TO FULL-LOAD COMPENSATING MEANS Filed May 15, 1965 4 Sheets-Sheet MAIN LOAD ,00 Z0] if? tan/ER REFERENCE LE VEL Z06 'MODULA 7'50 REFERNC VOLTS 206 LA? 22,2122 fij fmxzziefifion TIME fi/ R JE I United States Patent Ofifice 3,374,418 ALTERNATING CURRENT VOLTAGE REGULA- TOR INCLUDING SYSTEM NO-LOAD T FULL- LOAD COMPENSATING MEANS Robert M. Henderson, Williams Bay, and Richard Zechiin, Beloit, Wis., assignors to Fairbanks Morse Inc., New York, N.Y., a corporation of Delaware Filed May 13, 1965, Ser. No. 455,405 9 Claims. (Cl. 322-28) ABSTRACT OF THE DISCLOSURE An alternating current voltage regulator is disclosed including means for adjusting for the change in output of the generating system as the system goes from no-load to a full-load condition.

This invention relates to alternating current voltage regulators and, more particularly, to an improved alternating current voltage regulator, including means for compensating for voltage variations resulting from changes in the generating system load conditions.

It is a principal object of the present invention to provide an improved voltage regulator.

It is another object of the present invention to provide an AC voltage regulator including a sensing circuit and a power circuit in which the sensing circuit senses the voltage variation and couples a control signal to control the amount of current flowing through the field winding of an associated generator.

It is another object of the present invention to provide an AC voltage regulator arranged to provide a means for compensating for changes in the speed of operation of the associated machine.

It is another object of the present invention to provide an AC voltage regulator arranged to provide accurate voltage regulation for machines, including those which would be susceptible to changes of speed in operation.

It is yet another object of the present invention to provide an improved alternating current (AC) voltage regulator having circuit means for compensating for voltage Variation from system no-load to full-load conditions.

In the attainment of the foregoing objects, the invention provides an AC voltage regulator system having a circuit for sensing the voltage variation and a power circuit for applying a control current to the field Winding of the associated generator. The voltage regulator of the invention provides full half-cycle control of the power circuit with minimum time delay in relation to the operation of the sensing circuit. The sensing circuit comprises a unijunction transistor which is caused to conduct when the instantaneous control voltage is below a given reference level to thereby cause a signal to be coupled to fire a silicon controlled rectifier and permit current to flow through a series connected field winding of an exciter generator in such a manner as to tend to maintain the output of the generator at a predetermined value.

The invention further provides a circuit including means for compensating for the voltage variation so-called voltage droop from no-load to full-load operating conditions of the generator system. This compensating means is effective to provide additional control means to determine the amount of current caused to flow in the field winding of the generator system.

Other objects and advantages of the invention will become apparent from a consideration of the following specification in conjunction with the included drawings in which like reference characters refer to like elements throughout and in which:

FIG. 1 is a schematic diagram of one embodiment of an AC regulator in accordance with the invention;

3,374,418 Patented Mar. 19, 1968 FIGS. 2 and 3 show Waveforms useful in explaining the operation of the circuit of FIG. 1;

FIG. 4 is a schematic diagram of a second embodiment of the invention of the AC regulator in accordance with the invention;

FIG. 5 shows another waveform useful in explaining the operation of the circuit of FIGS. 1 and 4;

FIG. 6 is a schematic diagram of a generator field voltage supply circuit used in conjunction with the voltage regulators of FIGS. 1 and 2;

FIG. 7 is another embodiment of a generator field supply circuit;

FIG. 8 shows waveforms useful in tion of the circuits of FIGS. 6 and 7;

FIG. 9 is a schematic diagram of a third embodiment of the AC regulator in accordance with the invention and is arranged to compensate for changes in the speed of operation of the associated machine;

FIG. 10 is a schematic diagram of a fourth embodiment of the AC regulator in accordance with the invention also arranged to compensate for changes in the speed of operation of the associated machine; and

FIGS. 11, 12 and 13 are waveforms useful in explaining the operation of the circuits of FIGS. 9 and 10.

Referring to FIG. 1, the AC regulator 10 of the inven: tion is similar in general operation to conventional voltage regulators in the fact that the regulator senses the output voltage of an alternator or AC generator, compares the voltage sensed to a standard reference voltage, and changes the generator field current so as to reduce the difference between the sensed voltage and the reference voltage.

In FIG. 1, a three phase AC generator 11 has its phase or inductor windings 12, 13 and 14 connected in a Y or star-connected relation. The output terminals 17, 18 and 19 of the windings 12, 13 and 14 respectively, are connected to a main AC load through leads L1, L2, and L3. The terminal 17 also connects through lead 28 to the cathode of a silicon controlled rectifier (SCR) 30 for purposes to be hereinafter explained. The common connection or neutral terminal of the phase windings 12, 13 and 14 connects through lead 29 to one terminal 41 of the generator field Winding 31. The other terminal 44 of the generator field winding 31 connects to the anode of the SCR 30. The terminal 41 of the generator field winding 31 also connects through a line 40 as the common or reference line for the sensing circuit, generally labeled 25.

The power circuit, generally labeled 45, for the generator field winding 31 may be traced from the common or neutral terminal 120 through lead 29, generator field winding 31, anode 32 to cathode 33 of the SCR 30, leads 28 and phase winding 12 back to terminal 120.

A transformer 20 has its primary winding connected across terminals 18 and 19 of the phase windings 13 and 14. The secondary winding 22 of transformer 20 couples its out-put to the sensing circuit 25. One terminal of secondary winding 22 is connected to the anode of a series connected diode 47, and the other terminal of secondary winding is connected to neutral or common reference line 40. The cathode of diode 47 is connected at a terminal 49 to a parallel coupled capacitor 48. As is known, diode 47, capacitor 48 and voltage dividerSO comprise a wave shaping network for the remainder of the sensing circuit 25.

A variable resistor or voltage divider 50 is connected in parallel with capacitor 48. The terminal 49 and capacitor 48 also connect through a series resistor 51 to the emitter e of a unijunction transistor 52 which transistor includes a first or upper base B2 and a second or lower base B1. The base B2 of unijunction transistor 52 is serially connected through resistor 60 to the variable tap 58 of voltage divider 50. The base B1 of transistor 52 is connected in series with the primary winding 71 of a transformer 70 explaining the operain common reference line 40. The variable tap 58 of voltage divider 50 may also be connected in series through a resistor 61 and a diode 63 to the positive terminal of a battery 43. The negative terminal or battery 43 connects to the common or reference line 40. The resistor 61, diode 63 and battery 43 may be left out of the circuit, and are connected in the circuit of the embodiment shown for the specific purpose of providing automatic flashing, i.e., to provide automatic voltage buildup for machines with low residual voltages or machines connected to electrical loads when prime mover is started.

A series circuit of a Zener dide 54 and a second variable resistor or voltage divider 55 is connected in parallel with transistor 52. More particularly, the cathode of the Zener diode 54 is directly connected to the emitter e of the transistor 52 and the anode of diode 54 is connected to the voltage divider 55 which in turn is connected to common reference line 40. A circuit for providing a selected voltage reference level includes a second or control capacitor 57 connected in parallel with the Zener diode 54 and voltage divider 55. This latter circuit establishes the voltage control or reference level for the regulator. As is known, the capacitor 57 is charged by the output of transformer 20 and the Zener diode is effective to breakdown and conduct in the reverse direction as the voltage across capacitor 57 tends to rise above a selected level. Thus, a stable voltage reference level is maintained (see FIGS. 2 and 3).

The transformer 70 has a econdary winding 72 (for convenience in drawing, the secondary winding 72 is shown at the bottom left-hand portion of FIG. 1) which has one terminal connected to the control electrode 34 of the SCR 30 and the other terminal connected to lead 28 and terminal 17 of the phase winding 12; that is, winding 72 is connected across the control electrode 34 and the cathode electrode 33 of the SCR 30. As will be explained more fully heerinbelow, the transformer 70 is energizable to provide a control signal to cause or control the flow of current through the power circuit 45 and the generator field winding 31.

A resistor 73, which maintains the SCR 30 in conduction at zero field current, and a diode 75 are each connected in parallel with the generator field winding 31 and the diode 75 protects the SCR 30 by dissipating the induced potential or so-called inductive kick of the winding 31.

A capacitor 77 and a resistor 78 connect from terminal 44 of the generator field winding 31 in series through lead 65 to the tap 56 of the voltage divider 55, and also through lead 65A to the junction of voltage divider 55 and Zener diode 54. As will be discussed more fully hereinbelow, the capacitor 77 provides a means for compensating for voltage variations due to changes from a generator no-load to full-load operating conditions.

As is known, SCR 30 has the characteristic that the flow of current in the rectifier, i.e., from the anode 32 to the cathode 33 thereof, is initiated by the flow of current in the control electrode 34. Once current flow from the anode 32 to the cathode 33 is initiated, the control electrode 34 no longer controls the current flow through the SCR 30. In this latter condition, the current will continue to flow until the potentials on the anode 32 and the cathode 33 are changed to thereby stop conduction.

Referring now to the unijunction transistor 52, it is known that such a transistor will operate as a tapped resistor until the voltage on the emitter equals approximately 60% of the voltage between the base B2 and the base B1, in other words when Ve%.6 (V V where Ve is the voltage at the emitter e with respect to base B1; V is the voltage at the base B2; and V is the voltage at the base B1.

When the voltage Ve does equal approximately 60% of the voltage between base B2 and base B1, the unijunction transistor will start to conduct heavily and the resistance across the transistor 52 will decrease sharply. Thus, the unijunction transistor 52 offers a very sharp activation or turn-on operation at this aforesaid point or voltage level.

The operation of the circuit of FIG. 1 will now be described.

Referring first to the input position of the sensing circuit 25, the voltage transformer 20 is arranged to develop a voltage across its secondary winding 22 which is90 out of phase with the voltage developed across the phase winding 12. As mentioned above, the AC voltage from secondary winding 22 is rectified by diode 47 and filtered by capacitor 48, and provides a voltage to base B2 of transistor 52 which varies, as shown by waveform in PEG. 2 (see the second sheet of drawings). The waveform 80 is of the same wave shape as the voltage appearing at point 49, but is displaced in amplitude by the attenuation factor of voltage divider 50.

Thus, a voltage proportional to a voltage developed by the generator system is applied to the sensing circuit 25. The Zener diode 54 and resistor 51 are selected so that the voltage across the Zener diode 54 is essentially constant; thus applying a constant voltage to the emitter e of the unijunction transistor 52 once the capacitor 57 is charged. This voltage is indicated by the line labeled as Zener reference in FIG. 2. As mentioned above, if the voltage at the emitter e of transistor 52 is less than approximately 60% of the effective voltage between bases B2 and B1, then the transistor 52 acts as a high resistance. When the relative voltage on the emitter increases to this approximate 60% point, then the internal resistance from the emitter to base B1 of the unijunction transistor 52 decreases sharply to a low value. The capacitor 57 is thus permitted to discharge through the emitter e to base B1 circuit of transistor 52 and through the primary winding 71 of transformer 70. Accordingly, a voltage pulse is developed across the secondary winding 72 of transformer '70 and applied to the control electrode 34 of the SCR 30, and the SCR fires, i.e., is caused to conduct. Uuidirec tional current is thus permitted to flow in the power circuit 45, previously traced. As concerns the power circuit 45, the SCR 30 is connected in the circuit to block the negative half of the voltage waveform developed by phase winding 12 and, hence, only the positive half of the voltage from winding 12, i.e., the waveform labeled 81 (see FIG. 2) will tend to appear across the field winding 31.

Assume, a first operating condition, and consider that the generator is not loaded and thus requires only a small field current to maintain a regulated output, the conditions shown in FIG. 2 will exist. When the voltage developed across terminals 18 and 19 of phase windings 13 and 14 tends to decrease to a value which would tend to reduce the waveform 80 to a value lower than the Zener reference voltage, transistor 52 is biased to conduction, and a pulse is produced across transformer 70 thus firing the SCR 30 and causing a current numbered 91, and labeled as I (Field) in FIG. 2, to flow in the exciter generator field winding 31. The foregoing, in turn, causes the amplitude of the generating system output to increase. As shown, the amplitude of current flowing through the field winding 31 during the indicated condition is relatively low.

Assume, a second operating condition, and consider the generator is loaded to 100% with an eight-tenths A power factor; this requires that a higher magnitude current fiow through field winding 31 to hold the magnitude of the generating system output close to the output of the generator under no-load conditions. In a full-load condition, the SCR 30 will be caused to conduct sooner during the cycle, i.e., as soon as the voltage indicated by line 80 crosses or drops [below the Zener reference level. Note that the voltage waveform is effective to cause current to flow through the field winding 31 for a longer duration of time during each cycle. Accordingly, the current fiowing through the field winding 31, indicated by waveform 91, is of a higher magnitude than in the no-load condition of FIG. 5. This higher current flowing through the field winding 31 will tend to maintain the output voltage of the generating system at the selected level.

If the slope of the curves of waveform 80 is fiat, the output voltage will not change appreciably between no-load and full-load and thus close or good regulation will be obtained. Waveform 80 could be made quite flat by suitably adjusting the discharge characteristics, i.e., the discharge circuitry or capacitor 48; however, such adjustment might cause the generator system to become unstable. Thus, while it is necessary to have some slope in the voltage waveform 80 to assure stability of the system, the voltage variation from no-load to full-load should not exceed that required for good regulation.

The present invention provides a circuit which compensates for such voltage variation from no-load to fullload as will now be explained. As mentioned, if the generator is in a no-load operating condition, the curves or waveforms of FIG. 2 apply, and the SCR 30 fires only for a very small part of the cycle. Note that the voltage developed by the field winding 31 is effectively applied to the circuit consisting of capacitor 77, resistor 78 and a portion of voltage divider 55. The capacitor 77 thus charges through this circuit toward the voltage level of the field winding 31 during the time period indicated by pulses 90 in FIG. 2. As will be appreciated, the time during which capacitor 77 charges under such no-load conditions is short and therefore capacitor 77 reaches only a relatively low voltage. Then, during the portion of the cycle between the pulses 90, the capacitor 70 discharges to its initial state through the same path just traced (but in an opposite direction). If the voltage charge on capacitor 77 is of a small magnitude, the voltage developed across voltage divider 55 by this discharge of capacitor 77 during the discharge period will also be of a small magnitude. Thus, the voltage appearing across divider 55 will not have an appreciable elfect on the voltage reference level which is the voltage appearing across the series circuit of Zener diode 54 and the voltage divider 55. Note that the voltage reference level is also the voltage across the circuit from the emitter e of transistor 52 to the common reference line 40.

If, however, the generator is in a full-load condition, the curves or waveforms of FIG. 3 will be applicable. In this latter case the capacitor 77 will have time to charge to a higher amplitude voltage. During the period between pulses 90, the discharging capacitor 77 will cause a relatively higher current to flow in the voltage divider 55. The voltage developed across the divider 55 will be relatively higher in magnitude and will change the voltage reference level and, hence, the voltage present at the emitter e of transistor 52. The change in voltage effective at theemitter e of transistor 52 is, in a sense, to cause a higher current to flow through the field winding 31 to raise the output voltage of the generating system. The values of the voltages may be empirically adjusted, such that the change in voltage provided by capacitor 77 will cause a higher magnitude current to flow through the field winding 31 to hold the magnitude of the generating system output close to the output of the generator under noload conditions.

The time constant of the compensating circuit, including capacitor 77, resistor 78 and voltage divider 55, is long, compared to the time constant of the discharging circuit associated with capacitor 48; thus, capacitor 77, resistor 78 and voltage divider 55 have no appreciable effect on stability.

The invention also provides improved stability of the generating system, as will now be explained.

The voltage input to the sensing circuit 25 and the voltage input to the power circuit 45 are arranged to be in phase relationship. During the part of the cycle when the voltage is increasing to a positive peak, capacitor 48 is being charged through winding 22 of transformer 20 by the voltage developed across terminals 18 and 19' of phase windings 13 and 14, respectively. During the time when the voltage is decreasing the capacitor 48 is controlled only by the resistance in parallel with capacitor 48, i.e., the equivalent resistance of the entire control circuit 25, and this resistance is not necessarily related to the voltage developed across phase windings 13 and 14.

It can be seen that if a correction signal does not occur until later in the cycle and near the very end of the discharge time of capacitor 48, a long period of dead time exists. During the dead time, the generator voltage is changing and is no longer at the voltage previously measured, consequently, the system is correcting for a voltage that is no longer a true representation of existing conditions. To correct this factor, the sensing signal coupled through transformer 20 and the power signal obtained across terminals 17 and 20 from phase winding 12 is arranged to be in a phase such that a minimum of delay is provided between the action of measuring the voltage of the generator, and the corrective action of applying the voltage to the field winding 31. It has been found that a generating system can be stable with the phase relationship as described, but that if the power supplied to the field is delayed in excess of 90, instability may occur.

A second embodiment of a circuit of the invention is shown in FIG. 4. The circuits of FIGS. 1 and 4 are generally similar in structure and in operation. Also, as can be seen by comparison of FIGS. 1 and 4, the connections from and to the phase windings 12, 13 and 14 of the generating system are the same in both FIGS. 1 and 4. Note, too, that the polarity of the SCR 30 is reversed in FIG. 4 relative to FIG. 1.

A principal distinction of the circuits of FIGS. 1 and 4 is that in sensing circuit of FIG. 1 a control signal from the sensing circuit 25 of FIG. 1 is coupled through a transformer 70 to the control electrode 34 of the SCR while the sensing circuit of FIG. 4 couples a control signal directly from the base B1 of the unijunction transistor 52 to the control electrode 34 of the SCR 30, as will be explained more fully hereinbelow.

As noted, the circuits of FIGS. 1 and 4 are similar and hence for brevity in explanation, the components in FIGS. 1 and 4, which are connected and operate in substantially the same manner, are labeled with the same number in both FIGS. 1 and 4, and a description thereof will be repeated only as is necessary to understand the operation of the circuit of FIG. 4.

In FIG. 4, a diode 84 has its cathode connected to the left-hand terminal (as oriented in FIG. 4) of secondary winding 22, and its anode connected to the reference line 40. Diode 84 functions in the known manner to rectify the output of secondary winding 22 to provide positive going signals to the sensing circuit. The voltage divider is connected in series with another voltage divider 87, and the two dividers are connected in parallel with the capacitor 48. Note that in FIG. 4 the voltage divider of FIG. 1 is not employed. The voltage divider 87 has its movable tap 88 connected through series resistors 82 and to terminal 44, i.e., to the junction of the field winding 31 and the anode 32 of the SCR 30. The junction of resistors 82 and 85 is connected through a capacitor 83 to ground reference.

As mentioned, the output of transistor 52 is coupled from its base B1 through lead 89 to the control electrode 34 of the SCR 30.

Note that in FIG. 4, the compensating circuit (i.e., the circuit that compensates for output variations from no-load to full-load condition of the generating system), is essentially effective at the base B2 of transistor 52 rather than at the Zener diode 54 circuit as shown in FIG. 1. The operation of this latter circuit will be explained in detail hereinbelow.

In FIG. 4, the SCR 30 is connected with a polarity such that terminal 17 must be positive in order to permit the SCR to conduct. This is in contrast to FIG. 1 in which the terminal 17 must be relatively more negative than common terminal 120 to cause the SCR 30 to conduct. Otherwise, the operation of the two power circuits 45 of FIGS. 1 and 4 is essentially the same, i.e., the control electrode 34 initiates conduction of the SCR 30 and the SCR continues to conduct while the polarity at its anode 32 is positive with respect to its cathode 33.

As mentioned, the embodiment of FIG. 4 also provides a compensating circuit which includes capacitor 83, resistors 82 and 85, and voltage divider 87 to correct or compensate 'for output energy variation or droop due to changes in the load condition of the generating system.

For purposes of explaining the operation of the compensating circuit of FIG. 4, assume first that the generator is in a no-load condition. In this no-load condition, the SCR 30 fires for a very small part of the cycle and, co nsequently, the voltage applied to the anode 32 of the SCR 330 is almost a pure sine wave. This sine wave is also applied in series across the capacitor 83 and resistor 85, and hence to the circuit including resistor 82, tap 88 and the portion of divider 87 connecting tap 88 to ground reference. This sine Wave produces an average voltage on the capacitor 83 that is approximately zero volts in amplitude.

Now assume the generator becomes loaded. The SCR 30 will conduct for a longer period of time and the voltage applied to the resistor 82, resistor 85, and voltage divider 87 is that as shown in FIG. 5. The capacitor 83 now assumes a negative voltage essentially proportional to the direct current component of the wavefrom of FIG. 5, as indicated by line 197. This voltage is effective at the tap 88 of the voltage divider 87 and, accordingly, the amplitude of the voltage at tap 54 of divider 50 is decreased. Accordingly, the base B2 of transistor 52 which is connected to tap 54 will be effectively biased to cause the transistor 52 to conduct when the voltage at 49 is higher than the previously mentioned no-load voltage. Thus, the SCR 30 will be caused to conduct relatively sooner than in a no-load condition and, hence, more current will flow in the field winding 31. This causes a higher voltage to be developed across the phase windings 12, 13 and 14, and across transformer 20 to develop a higher voltage at terminal 49 to thereby reestablish the previous ratio of voltages on the unijunction transistor 52.

The compensating circuit parameters are arranged so that this voltage increase, which the compensating circuit causes the generating system to provide, just offsets the decrease of voltage due to the sloping characteristic of the capacitor 48 discharge. Thus, an essentially flat voltage output can be obtained from no-load to full-load operating conditions on the generator.

The time constant of the capacitor 83 circuit is long, compared to the time constant of the capacitor 48 circuits. Thus, the capacitor 83 circuit has no appreciable effect on the instantaneous operation of the capacitor 48 circuits.

For certain operating conditions it is advantageous to have the driving voltage, applied to the SCR 30 power circuit 45 of FIGS. 1 and 4, be a direct current voltage which is periodically reduced to zero for a very short time to permit the SCR to reset. Thus, a maximum amount of power can be transmitted for a given current and voltage rating of the SCR 30. To approach the foregoing type of operation, a three-phase voltage source with one-phase inverted can be utilized. In such a circuit three half wave signals 120 degrees apart are obtained and a period of zero voltage exists; this zero voltage period will allow resetting of the SCR. FIGS. 6 and 7 show two power circuits for obtaining the type of waveform desired.

In FIG. 6, diodes 94, 95 and 96 are connected in series with the respective phase windings 112, 113 and 114. More particularly, the anodes. of diodes 94, 95 and 96 are connected to the common terminal 120 and their cathodes are respectively connected to windings 94, 95 and 96. In FIG. 7, the diodes 97, 98 and 99 are connected in series with the respective phase windings 112, 113 and 114 with the cathodes of the diodes connected in common.

Also, a combination of generator windings and transformers may be used to obtain the circuits indicated in FIGS. 6 and 7. For example, windings 112 and 114 may be connected to the generator and phase winding 113 may be the secondary winding of a transformer.

It can be seen that this connection of the phase windings effectively adds the respective waveforms 101 developed thereby and provides a waveform envelope 103, as shown in FIG. 8, which approaches the aforementioned direct current driving voltage.

The circuits of FIGS. 6 and 7 may be combined with the voltage regulator circuits of FIGS. 1 and 4 as well as with the circuits of FIGS. 9 and 10 to be described. The circuits of FIGS. 6 and 7 are preferably usable with voltage regulators used in conjunction with generators of relatively large capacity.

Another embodiment of the invention is shown in FIG. 9. The circuit of FIG. 9 while it is, in general, similar to the circuit of FIG. 4, is particularly adapted to be used with machines which may be susceptible to changes in speed of operation. Accordingly, the circuit of FIG. 9 includes various components which were added to the circuit of FIG. 1 and also includes a circuit connection change over the circuit of FIG. 4, as will be described. Likewise, the operation of the circuit of FIG. 9 is, in general, similar to that of FIG. 4, as will be explained in detail hereinbelow.

Since the circuits of FIG. 4 and FIG. 9 are generally similar, only the circuit changes of FIG. 9 over FIG. 4 and the changes in mode of operation will be described.

Referring now to FIG. 9, one terminal of a resistor 121 is connected through lead 122 to terminal point 17 of the AC generator 11; the other terminal of resistor 121 is connected through lead 123 to the junction of resistor 61, wiper 58 of voltage divider 50, and resistor 60. A voltage from terminal point 17 of generator 11 is thus coupled to the base B2 of transistor 52 for purposes to be explained below.

A diode 124 has its anode connected to the non-ground terminal of the secondary winding 22 of transformer 20; the cathode of diode 124 is connected through lead 126 directly to the base B2 of transistor 52. Note also that the diode 84, also included in FIG. 4, is changed to have its anode connected to the non-ground terminal of the secondary winding 22; the rectifying operation of diode 84 is, of course, the same as in FIG. 4.

The operation of the circuit of FIG. 9 will now be described with reference to the waveforms of FIGS. 11, 12 and 13.

In FIG. 11, the positive waveforms 200 represent the rectified sence voltage obtained across the secondary winding 22 of transformer 20 during normal speed operation of the associated machine. The waveform obtained across the wave shaping network comprising capacitor 48 and voltage dividers 50 and 87 is represented by the upper or peak portion of waveforms 200 and by the solid line 201. The voltage coupled through voltage divider 50, tap 58, and resistor 60 to the base B2 of transistor 52 is indicated by the waveform labeled 201'; and as can be appreciated, waveform 201' is the same as waveform 201 attenuated by a given factor. The voltage reference level arranged to be provided by the Zener diode 54 and capacitor 57 to the emitter e of transistor 52 is indicated by the horizontal line 202.

The power waveform 205, i.e., the voltage output from the winding 12 of generator 11, is displaced in phase from the sense waveform 200 obtained across transformer 20. In operation, it is a portion of the power waveform 205 energ i.e., the exciter field voltage indicated by the heavy cross hatched area 203 of power waveform 205 which will energize the field winding 31 to control the output of the generator 11.

During normal speed operation of the associated machine, the signal represented by waveform 205 will provide an ex-citer field voltage indicated by the cross hatched area 203 in FIGS. 11 and 12. Should the associated machine, for some reason, slow down its speed of operation, the time interval of each half cycle of the sense voltage waveforms 200 and of the power waveforms 205 will increase as shown in FIG. 12; i.e., each wave cycle will tend to spread out in time. For purposes of clarity, in the drawing of FIG. 12, the half cycle waveforms 200 and power waveforms 205, which represent the similarly numbered waveforms as in FIG. 11, are shown in time expanded scale.

Note that in FIG. 12, the sense waveforms 200 indicate a normal operating condition; and the sense waveform 200" shown by the dotted lines indicates a machine slow-down operating condition. As mentioned above, the power waveform is 90 out of phase with the sense waveform and, hence, the power waveforms 205 and 205 correspond respectively to the normal sense waveform 200, and the machine slow-down sense waveform 200".

The sense waveform 201 which is the portion of the sense waveform provided by the discharging of capacitor 48 through the associated resistor network is not affected by changes in generator output with changing speed. Likewise, waveform 201 which is of the same shape as waveform 201 but attenuated by a given factor, is not affected by changes in speed. Therefore, for a given generator voltage output, the time interval for the waveform 201' to decrease to point 210 where it intersects with the Zener reference level 202 to cause transistor 52 to conduct and thus permit field current to flow in winding 31 is the same regardless, or independent of any change in speed of operation. Accordingly, as the machine tends to slow down, and as the power cycle spreads out in time as indicated by dotted waveform 205', the field power increases. This tends to raise the generator regulator volt age, as is indicated by the entire cross hatched area 203 and 203' of waveform 205'. The power requirements of the prime moved depend on the kilowatt output of the generator. The kilowatt output operating into the load is the function of the voltage output times the line amperes. As the machine slows down, more torque is required to supply the same kilowatt load. This initial slow-down tends to continue and becomes worse because of the increased demands of the torque output. Further, if an inertia load is connected to the generator, the inertia load acts as a forced vibrator; hence, speed oscillation and voltage oscillation may occur as the engine recovers speed.

The circuit of FIG. 9 is specifically arranged to provide a corrective action to compensate for any decrease in the speed of the associated engine.

In order to compensate for any variation in associated generator speed, a voltage is connected from terminal point 17 of generator 11 through lead 122, resistor 121, lead 123, and resistor 60 to the base B2 of the transistor 52.'The voltage connected tobase B2 is a sine wave 206 which is 180 out of phase with the power waveform 205. The voltage waveform 206 will modulate the voltage at the base B2 and thus will cause a variation in the voltage level at which the transistor 52 is caused to conduct. Accordingly, if the power waveform 205 is delayed, the waveform 206 will also be delayed or shifted correspondingly, see both FIGS. 11 and 12. The reference level, at which the transistor 52 is caused to conduct, is thus modulated to compensate for any shift or delay of the power waveform 205, see points 210' and 210".

The net effect of the foregoing mode of operation is to control the firing of the transistor 52 dependent upon the modulated voltage developed at point 17 of generator 11. Thus, as the power waveform 205 is delayed, the modulation will likewise be delayed a same period and the reference level at the base B2 will remain at the same position independent of the speed of the engine.

A second signal voltage is coupled from winding 22 of transformer 20 through a diode 124 directly to the base B2 of transistor 52 as indicated by the dotted lines 200' 10 in FIG. 11. During the peak portion of the sence waveform 200, a positive voltage is coupled to base B2; and, of course, the same voltage is also coupled to the wave shaping network including capacitor 48. As will be appreciated, the composite waveform effective at the base B2 of transistor 52 is indicated by the dotted waveform 200 during the peak portion of the waveform 200, and discharge waveform 201' provided by capacitor 48 and voltage divider 50 during the interval between the peak portions of the waveforms 200.

This direct application of the peak portion of waveform 200' to the base B2 is found desirable to provide accurate control of the firing of transistor 52. It has been determined that, when Zener reference level 202 is modulated by the voltage waveform 206, there is an unstable time period between the peak point 212 of waveform 201', i.e., the voltage effective at the base B2 of transistor 52, and point 213, the capacitor 48 voltage level. As ill-ustrated in FIG. 13, there is a critical time period, during which the slope of the waveform 201' is almost the same as the slope of the modulating voltage 206. The foregoing may cause the firing point of transistor 52 to be unstable since a very small voltage change can cause wide changes in the firing time of the transistor 52. In order to prevent the foregoing unstable condition from existing and to more precisely control the firing of the transistor 52, the peak portion of the sense voltage 200' is coupled directly from winding 22 through diode 124 to base B2. The composite waveform effective at the base B2 of transistor 52 is thus waveform 200' and the capacitor discharge voltage waveform 201'. A high voltage on base B2 thus prevents the transistor 52 from firing during the time period between the peak point 212 of the waveform 201' and the capacitor charging level at point 213.

Referring now to FIG. 10 which shows still another embodiment of the invention, the circuit of FIG. 10 while it is, in general, similar to the circuit shown in FIG. 1, is particularly adapted to be used with machines which may be susceptible to changes in speed of operation. Accordingly, the circuit of FIG. 10 includes various components which were added to the circuit of FIG. 1, and also includes a circuit connection change from the circuit of FIG. 1, as will be described.

Since the circuits of FIG. 1 and FIG. 10 are generally similar, only the circuit changes of FIG. 10 over FIG. 1 will be described. More particularly, in FIG. 10, resistor 129 is connected through lead 131 to terminal 17 of the AC generator 11; the other terminal of resistor 129 is connected through lead 132 to the junction point of the voltage regulator 55 and Zener diode 54. A diode has its anode connected to the junction of diode 47 and the secondary winding 22 of transformer 20; and, the cathode of diode 130 is connected through lead 133 to base B2 of transistor 52. Note also that the circuit of FIG. 10, lead 65 is connected only to the wiper 56 of voltage regulator 55 and is not connected to the junction of Zener diode 54 and the voltage regulator 55 as in FIG. 1. I

The operation of the circuit of FIG. 10 is essentially the same as that of FIG. 9. A principal difference in the operation of the circuits of FIGS. 9 and 10 is that in FIG. 10 the modulating voltage from point 17 of generator 11 is coup ed to the junction of the Zener diode 54 and voltage divider 55. The modulating voltage is-thus effective at the emitter electrode e of transistor 52; however, the effect of the modulating voltage on the operation of the circuit of FIG. 10 is the same as that in the circuit of FIG. 9.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention. Also, the theory of operation of FIGS. 9 and 10 is generally applicable andneed not 1 1 be limited to a slow-down of the associated machine.

We claim:

1. A voltage regulator for an alternating current generator system having phase windings and a field winding, said regulator including a compensating circuit for adjusting for droop of the output of said generating system as said system goes from a no-load to a full-load condition comprising, in'combination:

(a) a sensing circuit responsive to changes in the output of said generator system;

(b) said sensing circuit including means for developing a direct current voltage of an amplitude dependent on the alternating current output of said generator system;

(c) circuit means for coupling an input voltage proportional to said direct current voltage to said sensing circuit;

(d) means for providing a voltage at a selected reference level to said sensing circuit;

(e) electronic switching means associated with said field winding;

(f) means for coupling a signal from said sensing circuit to said switching means to thereby permit current flow in said field winding to maintain the output of said generator system between predetermined limits;

(g) capacitor means chargeable in response to current flow through said field winding; and

(h) means for selectively coupling the voltage appearing across said capacitor means to combine said voltage with said reference voltage to thereby compensate for said droop.

2. A voltage regulator as in claim 1, wherein,

(a) said capacitor means is charged during periods of current flow through said field winding and said capacitor is discharged during the periods between current flow through said field Winding against a minimal back voltage; and

(b) the discharge path for said capacitor means includes an impedance means connected in series with the reference voltage whereby the voltage appearing across said capacitor means is combined with said reference voltage to thereby compensate for said droop.

3. A regulator as in claim 2 comprising a compensating circuit for adjusting for droop of the output of said generating system as said system goes from a no-load to a full-load condition, said compensating circuit including:

(a) a means for developing a reference voltage comprising:

(b) a resistance unit and a Zener diode connected in series and in parallel with a first capacitor;

(c) a second capacitor having one electrical terminal connected to one electrical terminal of said field winding and its other electrical terminal connected to one electrical terminal of said resistance unit,

(d) means connecting the other electrical terminal of said resistance unit to the other electrical terminal of said field winding whereby the voltage developed across said field winding is effective across said capacitor and is combined with said reference level voltage to adjust said reference level voltage to compensate for said droop.

4. A voltage regulator, as in claim 1, comprising (a) a unijunction transistor having an emitter and two base electrodes;

(b) voltage divider means connected in parallel with the emitter to first electrode current path of said transistor;

() first tap means on said voltage divider means connecting to said second electrode;

((1) second tap means connecting said voltage divider means to one terminal of said field winding;

(e) capacitor means connected to said second tap means and in parallel to a portion of said voltage divider means, said capacitor being chargeable during the period of current fiow through said field winding, and

(f) a discharge path for said capacitor including a portion of said voltage divider whereby during the period of time when current does not flow through said field winding, the capacitor discharges through said path whereby the capacitor voltage is combined with the voltage appearing across said voltage divider means, to compensate or adjust for any droop in the output of said generating system.

5. A voltage regulator for a multiphase alternating current generator system having phase windings and a field winding, said regulator comprising:

(a) a sensing circuit connected to receive a signal of a first phase from said phase windings;

(b) said sensing circuit including means for developing a direct current voltage of an amplitude dependent on said first phase input;

(c) said sensing circuit including a unijunction transistor having an emitter and first and second base electrodes;

(d) means for coupling a voltage proportional to said direct current voltage to said second base electrode;

(e) means for providing a reference voltage at a selected level to said emitter;

(f) means for coupling a signal of a second phase from said phase windings to modulate said reference voltage;

(g) means for coupling the output of said transistor to a control device for enabling current to fiow through said field winding to enable said device to conduct to thereby permit current flow in said field winding to maintain the output of said generator system between predetermined limits; and

(11) said transistor being rendered conductive when the ratio between said direct current voltage applied thereto and said modulated reference voltage changes from a selected value.

6. A voltage regulator as in claim 5, wherein:

(a) means are provided for connecting a signal from said phase windings of second phase to said transistor for modulating said first reference level.

7. A voltage regulator as in claim 5, wherein:

(a) means are included for connecting a voltage of said first phase coupled directly from said input to said transistor, said directly coupled voltage preventing said transistor from conducting during a portion of said first phase input to said sensing voltage.

8. A voltage regulator as in claim 5, wherein:

(a) a transformer is connected across said phase windings to develop a voltage of a first phase;

(b) said transformer providing a signal to said sensing circuit; and

(c) means for coupling said transformer to provide a signal of said first phase directly to said transistor for preventing said transistor from conducting during the peak portion of said first phase.

9. A voltage regulator for a multiphase alternating current generator system having phase windings and a field winding, said regulator comprising:

(a) a sensing circuit responsive to changes in the output of said generator system;

(b) transformer means for coupling a signal of a first phase to said sensing circuit;

(c) said sensing circuit including capacitor means for developing a voltage of an amplitude dependent on the amplitude of said first phase signal;

((1) a unijunction transistor having an emitter and first and second base electrodes;

(e) circuit means for coupling the voltage developed across said direct current voltage to said second base electrode;

(f) means for providing a voltage at a selected reference level across the emitter to said first base elec- 13 trode, said transistor being rendered conductive when the ratio between said input voltage and said reference voltage changes from a selected value;

(g) means for coupling a signal directly from said transformer to said second electrode to prevent said transistor from conductin during selected cycle periods;

(h) means for coupling a signal of a second phase to modulate said reference level applied to said transistor to control the firing of said transistor in relation to the phase of said generator system output;

(i) a silicon controlled rectifier having an anode, a cathode and a control electrode, said rectifier having its anode to cathode circuit connected to selected terminals on said phase windin with said field winding; and

(j) means for coupling a signal from said transistor to the control electrode of said rectifier to enable said rectifier to conduct and to thereby permit current to flow in said field winding t0 thus maintain the output of said generator system between predetermined limits.

References Cited UNITED STATES PATENTS 3,008,082 11/1961 'Schlicher 322-28 3,151,288 9/1964 Avizienis et al. 322-28 3,214,599 10/1965 Wellford 322-28 3,226,626 12/1965 Moore 32228 gs and being in Series 15 -MILTON O. HIRSHFIELD, Primary Examiner.

R. V. LUPO, Assistant Examiner.

Patent No. 3,374,418

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION March 19 1968 Robert M. Henderson et all.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 11, line 45, the claim reference numeral "2" shonld read 1 Signed and sealed this 16th day of December 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR. 

